The present invention relates generally to silicate minerals, and more particularly to sedimentary mica.
Mica comprises a class of silicate minerals having perfect basal cleavage and widely varying chemical compositions. The most common species of mica are muscovite KAl2(AlSi3O10) (OH) 2, phlogopite K(Mg,Fe)3(AlSi3O10) (OH)2, and biotite K(Fe,Mg)3(AlSi3O10) (OH)2. These species are rock forming minerals occurring within a variety igneous, metamorphic and sedimentary rocks, as well as in many mineral deposits.
Mica has a variety of commercial uses in both sheet form and in flake form. Flake mica is used as both a filler and coating in paint, wallpaper, plastics, cosmetics, and a variety of other products. Flake mica is typically produced by grinding crude mica, which is typically in the form of books or stacks of numerous mica platelets bonded together in a face-to-face configuration. The grinding process breaks up these stacks to produce individual platelets of mica. Grinding is typically performed in Chaser mills, and the like, having rollers or balls that roll over the mica for a period of generally six to eight hours per ton. Delamination enhances the sheen and slip of the mica, and makes a more desirable product.
The mills currently used are designed to grind coarse mica ore derived from igneous intrusive rock and metamorphic schist wherein the mesh size is generally greater than or equal to one-hundred (100) mesh. Unfortunately, sedimentary mica, due to its naturally fine size (generally less than or equal to 100 mesh), will not delaminate in these mills at a production rate that is economical. Consequently, sedimentary mica is typically not used to produce mica flakes.
In addition, the kaolin and sand industries typically avoid mining clays containing sedimentary mica. The platey nature of sedimentary mica causes problems during screening steps in kaolin production processes. The kaolin industry typically processes kaolin having a mesh size less than or equal to three-hundred-twenty-five (325) mesh. Consequently, sedimentary mica contained within the kaolin slurry often causes blinding of the screens, thereby hampering production. In addition, ultra-fine mica also retards slurry makedown and is detrimental to Brookfield viscosity, because of its platey shape and dielectric properties.
The sand industry avoids mining sand from areas containing a high percentage of sedimentary mica. Unfortunately, sedimentary mica is present in most sand deposits. Consequently, during sand production, a majority of the washing process steps are for the purpose of removing silts and sedimentary mica due to their detrimental properties. Because of the friable, flexible, and platey nature of sedimentary mica, the dried strength of mortar and concrete is reduced when sedimentary mica is present. Furthermore, because of its high surface area, sedimentary mica platelets are highly absorptive of water. Consequently, the presence of sedimentary mica in concrete sand may cause the water demand for a mixture to increase beyond normal levels. For certified concrete mixtures, water added beyond specifications may render the concrete unusable.
It is therefore an object of the present invention to provide economical methods for continuously delaminating sedimentary mica.
It is another object of the present invention to economically produce a superior grade of flake mica product from sedimentary mica, thereby creating a demand for sedimentary mica, which has, until now, been practically non-existent.
These and other objects are accomplished, according to the present invention, by systems and methods for producing a delaminated sedimentary mica product. A substantially white delaminated mica product, comprising a plurality of sedimentary mica flakes, substantially all of which are less than forty-four microns (44xcexc), and having a bulk density of between about five and one-half pounds per cubic feet and eleven pounds per cubic feet (5.5-11 lbs/ft3), a high aspect ratio, and a G.E. brightness between about seventy-five (75) and ninety (90), may be produced, according to the present invention.
A first slurry of crude sedimentary mica and water is prepared, and shear forces are applied thereto to delaminate the mica therein into flakes. The application of shear forces to the first slurry preferably includes rotating a plurality of arcuate blades within a confined cylindrical delaminating chamber containing the first slurry, such that the first slurry is forced between an outer portion of each blade and the chamber. The outer portion of each blade is spaced from and substantially concentric with a portion of the delaminating chamber. Preferably, the first slurry comprises mica particles larger than about 325 mesh size. In addition, the first slurry may have a solids to water ratio in the range of about fifty to seventy percent (50%-70%).
The delaminated mica flakes are mixed with water to produce a second slurry. The second slurry may have a solids to water ratio in the range of about 10%-30%. Fine mica flakes are separated from coarse mica flakes within the second slurry, preferably via a centrifuge, and the separated fine mica flakes are dried, preferably to a moisture content of one percent (1%) or less. Impurities may be removed from the separated fine mica flakes after drying. The dried mica flakes may then be further-classified according to particle size.
Additionally, shear forces may be applied to the coarse mica flakes separated within the second slurry to delaminate these flakes further. These delaminated mica flakes are mixed with water to produce a third slurry. Fine mica flakes are then separated from coarse mica flakes within the third slurry, preferably via a centrifuge, and the separated fine mica flakes are dried, preferably to a moisture content of 1% or less. The third slurry has a solids to water ratio in the range of about ten to thirty percent (10%-30%). The step of applying shear forces to the coarse mica flakes preferably is carried out as described above, via a plurality of arcuate blades rotating within a confined cylindrical chamber. Additional separation steps may be performed followed by additional shear force delamination, as desired.
The present invention is advantageous because otherwise unused sedimentary mica can be processed to produce a superior grade of mica flake product economically. The process according to the present invention, produces mica flakes that are clearly differentiated from other wet ground mica flakes because of better brightness and color, lower bulk density, and higher surface area.
Because of the manner in which shear forces are applied to the mica books, delamination is obtained quickly as compared with prior art delamination methods. Consequently, sedimentary mica, other low abrasion minerals, and any other materials requiring delamination or particle size reduction can be delaminated and processed on a continuous basis using the methods of the present invention. Furthermore, the present invention is advantageous in that it does not require the use of grinding media.